The present invention relates to lawn mowers and more particularly to height adjustment mechanisms for such mowers.
Household lawn mowers comprise a cutting deck upon which is mounted a motor. The motor can be either an electric motor powered by either a main electricity supply or a battery or an internal combustion engine. The motor rotatingly drives a cutting blade mounted below the cutting deck about a substantially vertical axis. The cutting blade cuts the grass beneath the deck as it rotates. The cutting deck is commonly mounted on wheels or rollers. The wheels can either have a fixed direction of travel so that the lawn mower moves over the lawn in a forward and reverse direction, or can be castor wheels which are able to freely swivel so that the mower can travel over the lawn in any direction of travel.
It is desirable to have the height of the cutting blade adjustable in relation to the surface of the lawn. This allows the grass to be cut to differing heights. One common way of achieving this is by having the cutting deck of the lawn mower mounted on the wheels or rollers in such a manner that the height of the deck, and hence the height of the cutting blade, is adjustable relative to the wheels.
Such mechanisms include mounting the axles of the wheels or rollers on the ends of levers which are pivotally mounted onto the deck and which are capable of being releasably locked into a plurality of angular positions. The height of the cutting deck in relation to the wheels or rollers is dependent upon the angle of pivot of the levers. Interconnecting bars can be added between the levers to ensure that the levers pivot in unison so that the height adjustment of the wheels is uniform.
In one type of mower, the forward and rear axles are mounted on the end levers which are pivotally mounted on the cutting deck which are parallel and are interconnected by a bar so that they pivot in unison. However, the forward rear axles pivot about their axes in the same direction. U.S. Pat. No. 4,835,952 shows a mower having a typical design of height adjusting mechanism. In U.S. Pat. No. 4,835,952 the front axle is mounted on to arms of two bell cams which are pivotally mounted onto the body of the mower at their apexes. The second arm of the bell cams project in a generally upward direction. The rear axle is mounted in a similar fashion. Two interconnecting bars interconnect between the second arms of the front and rear bell cams. As the front bell cams pivot, the rear bell cams also pivot in the same direction thus lowering or highering the body of the mower uniformly.
However, such designs are bulky taking up valuable space on the mower because it is necessary for the interconnecting bars to project beyond the wheels. In addition, the length of the interconnecting bars has to be approximately the same as the distance between the front and rear wheels if the rate which the height of the deck rises above each wheel is to be constant.
According to the present invention, a lawn mower comprises a cutting deck mounted on at least first and second wheel assemblies. The first and second wheel assemblies comprise, respectively, first and second height adjustment mechanisms. The first height adjustment mechanism comprises a first pivoting mechanism pivotal about a first axis for adjustment of the height of the deck above the first wheel assembly. The second height adjustment mechanism comprises a second pivoting mechanism pivotal about a second axis, parallel to the first axis, for adjustment of the height of the deck above the second wheel assembly. A connection is formed between the first and second pivoting mechanisms for pivoting the first and second pivoting mechanisms in opposite directions about the first and second axis, respectively. By constructing the height adjustment mechanisms in this fashion, it can provide a compact construction. It can also enable the height adjustment mechanism to be located between the wheel assemblies thus reducing the amount of mechanical linkage required.
Preferably, each of the pivoting mechanisms raise the height of the deck by substantially equal amounts when pivoted through any part of their full range of pivotal movement.
Preferably, the first pivoting mechanism is pivotally connected at a first point away from its (xe2x80x9cfirstxe2x80x9d) pivot axis to an end of an interconnecting bar. The second pivoting mechanism is pivotally connected at a second point away from its (xe2x80x9csecondxe2x80x9d) pivot axis to the other end of the interconnecting bar. This can provide a simple and reliable construction.
The length of the interconnecting bar can be less than the distance between the axes of pivot of the pivoting mechanisms. This provides the advantage that the points of articulation at the ends of any interconnecting bar joining the pivoting mechanisms can lie between the pivoting mechanisms while allowing substantially equal vertical movement of the different height adjustment mechanisms.
Preferably, the first point connection of the bar to the first pivoting mechanism is spaced from the first axis in a first direction parallel to a plane extending though the first and second axes. And the second point connection of the bar to the second pivoting mechanism is spaced from the second axis in a second direction opposite the first direction. This can enable the length of the interconnecting rod to be reduced so that it is less than the distance between the axes of pivot. In addition, the interconnecting bar does not have to project pass any of the wheel assemblies when moved through its full range of positions and thus avoids taking up valuable space.
Each pivoting mechanism can be pivotally connected to the interconnecting bar via a rod which is rigidly attached to the pivoting mechanism and which preferably projects perpendicularly away from the axis of pivot of the pivoting mechanism. In a direction perpendicular to the plane which passes through both axes of pivot of the pivoting mechanisms, the two rods ideally project in opposite directions to each other and preferably in a direction parallel to a plane which passes through both axes of pivot, towards each other.
Each pivoting mechanism can comprise at least one lever pivotally mounted on the cutting deck and connected with the wheel assembly. And ideally, the lever of each mechanism are configured to move as a mirror image of each other in the plane located equidistantly between the two axes of pivot of the levers. The levers can project from their axis of pivot in a direction parallel to a plane which passes through both axes of pivot away from each other. This can result in a very compact yet simple height adjustment mechanism. The whole of the interconnecting mechanism is located between the wheel assemblies throughout its fill range of movement.